Bug 216404

Comment 1 Jan Beich 2017-01-23 12:01:02 UTC

(In reply to Jan Beich (mail not working) from comment #0)
> regressed by: https://github.com/llvm-mirror/libcxx/commit/120401a4e033

Oops, that was a different issue. Here's the first bad for comment 0:

https://github.com/llvm-mirror/libcxx/commit/39c36254e556

Comment 2 Dimitry Andric 2017-01-23 20:29:42 UTC

(In reply to Jan Beich (mail not working) from comment #1)
> (In reply to Jan Beich (mail not working) from comment #0)
> > regressed by: https://github.com/llvm-mirror/libcxx/commit/120401a4e033
> 
> Oops, that was a different issue. Here's the first bad for comment 0:
> 
> https://github.com/llvm-mirror/libcxx/commit/39c36254e556

Yes, I replied to Eric on that commit on the cfe-commits mailing list.  It would be nice if there is a fallback for pre-C++11.  Basically omitting the "template <class = void>" line for it would be enough, I think.

Although, the simple test case from that commit:

#include <string>
#include <cassert>

int main()
{
  // Test that assignment from {} and {ptr, len} are allowed and are not
  // ambiguous.
  {
    std::string s = "hello world";
    s = {};
    assert(s.empty());
  }
  {
    std::string s = "hello world";
    s = {"abc", 2};
    assert(s == "ab");
  }
  return 0;
}

will not compile with g++ (4.9 or 5.4) in pre-C++11 mode, because of an ambiguity:

$ g++5 -nostdinc++ -I/usr/include/c++/v1 -c test.cpp
test.cpp: In function 'int main()':
test.cpp:10:10: warning: extended initializer lists only available with -std=c++11 or -std=gnu++11
     s = {};
          ^
test.cpp:10:7: warning: extended initializer lists only available with -std=c++11 or -std=gnu++11
     s = {};
       ^
test.cpp:10:7: error: ambiguous overload for 'operator=' (operand types are 'std::__1::string {aka std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >}' and '<brace-enclosed initializer list ')
In file included from test.cpp:1:0:
/usr/include/c++/v1/string:2007:1: note: candidate: std::__1::basic_string<_CharT, _Traits, _Allocator>& std::__1::basic_string<_CharT, _Traits, _Allocator>::operator=(const std::__1::basic_string<_CharT, _Traits, _Allocator>&) [with _CharT = char; _Traits = std::__1::char_traits<char>; _Allocator = std::__1::allocator<char>]
 basic_string<_CharT, _Traits, _Allocator>::operator=(const basic_string& __str)
 ^
/usr/include/c++/v1/string:825:19: note: candidate: std::__1::basic_string<_CharT, _Traits, _Allocator>& std::__1::basic_string<_CharT, _Traits, _Allocator>::operator=(std::__1::basic_string<_CharT, _Traits, _Allocator>::__self_view) [with _CharT = char; _Traits = std::__1::char_traits<char>; _Allocator = std::__1::allocator<char>; std::__1::basic_string<_CharT, _Traits, _Allocator>::__self_view = std::__1::basic_string_view<char>]
     basic_string& operator=(__self_view __sv)  {return assign(__sv);}
                   ^
/usr/include/c++/v1/string:831:45: note: candidate: std::__1::basic_string<_CharT, _Traits, _Allocator>& std::__1::basic_string<_CharT, _Traits, _Allocator>::operator=(const value_type*) [with _CharT = char; _Traits = std::__1::char_traits<char>; _Allocator = std::__1::allocator<char>; std::__1::basic_string<_CharT, _Traits, _Allocator>::value_type = char]
     _LIBCPP_INLINE_VISIBILITY basic_string& operator=(const value_type* __s) {return assign(__s);}
                                             ^
/usr/include/c++/v1/string:1986:1: note: candidate: std::__1::basic_string<_CharT, _Traits, _Allocator>& std::__1::basic_string<_CharT, _Traits, _Allocator>::operator=(std::__1::basic_string<_CharT, _Traits, _Allocator>::value_type) [with _CharT = char; _Traits = std::__1::char_traits<char>; _Allocator = std::__1::allocator<char>; std::__1::basic_string<_CharT, _Traits, _Allocator>::value_type = char]
 basic_string<_CharT, _Traits, _Allocator>::operator=(value_type __c)
 ^
/usr/include/c++/v1/string:835:19: note: candidate: std::__1::basic_string<_CharT, _Traits, _Allocator>& std::__1::basic_string<_CharT, _Traits, _Allocator>::operator=(std::initializer_list<typename _Traits::char_type>) [with _CharT = char; _Traits = std::__1::char_traits<char>; _Allocator = std::__1::allocator<char>; typename _Traits::char_type = char]
     basic_string& operator=(initializer_list<value_type> __il) {return assign(__il.begin(), __il.size());}
                   ^
test.cpp:15:18: warning: extended initializer lists only available with -std=c++11 or -std=gnu++11
     s = {"abc", 2};
                  ^
test.cpp:15:7: warning: extended initializer lists only available with -std=c++11 or -std=gnu++11
     s = {"abc", 2};
       ^
test.cpp:15:7: error: ambiguous overload for 'operator=' (operand types are 'std::__1::string {aka std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >}' and '<brace-enclosed initializer list ')
In file included from test.cpp:1:0:
/usr/include/c++/v1/string:2007:1: note: candidate: std::__1::basic_string<_CharT, _Traits, _Allocator>& std::__1::basic_string<_CharT, _Traits, _Allocator>::operator=(const std::__1::basic_string<_CharT, _Traits, _Allocator>&) [with _CharT = char; _Traits = std::__1::char_traits<char>; _Allocator = std::__1::allocator<char>]
 basic_string<_CharT, _Traits, _Allocator>::operator=(const basic_string& __str)
 ^
/usr/include/c++/v1/string:825:19: note: candidate: std::__1::basic_string<_CharT, _Traits, _Allocator>& std::__1::basic_string<_CharT, _Traits, _Allocator>::operator=(std::__1::basic_string<_CharT, _Traits, _Allocator>::__self_view) [with _CharT = char; _Traits = std::__1::char_traits<char>; _Allocator = std::__1::allocator<char>; std::__1::basic_string<_CharT, _Traits, _Allocator>::__self_view = std::__1::basic_string_view<char>]
     basic_string& operator=(__self_view __sv)  {return assign(__sv);}
                   ^
/usr/include/c++/v1/string:835:19: note: candidate: std::__1::basic_string<_CharT, _Traits, _Allocator>& std::__1::basic_string<_CharT, _Traits, _Allocator>::operator=(std::initializer_list<typename _Traits::char_type>) [with _CharT = char; _Traits = std::__1::char_traits<char>; _Allocator = std::__1::allocator<char>; typename _Traits::char_type = char]
     basic_string& operator=(initializer_list<value_type> __il) {return assign(__il.begin(), __il.size());}
                   ^

On the other hand, it also does not compile when you use its own libstdc++, in that case:

$ g++5 -c test.cpp
test.cpp: In function 'int main()':
test.cpp:10:10: warning: extended initializer lists only available with -std=c++11 or -std=gnu++11
     s = {};
          ^
test.cpp:10:7: warning: extended initializer lists only available with -std=c++11 or -std=gnu++11
     s = {};
       ^
test.cpp:10:7: error: ambiguous overload for 'operator=' (operand types are 'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' and '<brace-enclosed initializer list>')
In file included from /usr/local/lib/gcc5/include/c++/string:52:0,
                 from test.cpp:1:
/usr/local/lib/gcc5/include/c++/bits/basic_string.h:550:7: note: candidate: std::__cxx11::basic_string<_CharT, _Traits, _Alloc>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::operator=(const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]
       operator=(const basic_string& __str)
       ^
/usr/local/lib/gcc5/include/c++/bits/basic_string.h:558:7: note: candidate: std::__cxx11::basic_string<_CharT, _Traits, _Alloc>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::operator=(const _CharT*) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]
       operator=(const _CharT* __s)
       ^
/usr/local/lib/gcc5/include/c++/bits/basic_string.h:569:7: note: candidate: std::__cxx11::basic_string<_CharT, _Traits, _Alloc>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::operator=(_CharT) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]
       operator=(_CharT __c)
       ^
test.cpp:15:18: warning: extended initializer lists only available with -std=c++11 or -std=gnu++11
     s = {"abc", 2};
                  ^
test.cpp:15:7: warning: extended initializer lists only available with -std=c++11 or -std=gnu++11
     s = {"abc", 2};
       ^

Comment 3 commit-hook 2017-01-23 22:11:31 UTC

A commit references this bug:

Author: dim
Date: Mon Jan 23 22:10:57 UTC 2017
New revision: 312673
URL: https://svnweb.freebsd.org/changeset/base/312673

Log:
  Pull in r292830 from upstream libc++ trunk (by Eric Fiselier):

    Fix GCC C++03 build by hiding default template argument in C++03

  This allows the graphics/GraphicsMagic to compile with gcc 4.9 and
  libc++.

  PR:		216404

Changes:
  projects/clang400-import/contrib/libc++/include/string

Comment 4 Dimitry Andric 2017-01-29 16:31:33 UTC

Should be fixed now, after r312673.